Abstract

The design of an instrument deployed in a project studying the high altitude Himalayan migrations of bar-headed geese (Anser indicus) is described. The electronics of this archival datalogger measured 22 × 14 × 6.5 mm, weighed 3 g, was powered by a ½AA-sized battery weighing 10 g and housed in a transparent biocompatible tube sealed with titaniumelectrodes for electrocardiography (ECG). The combined weight of 32 g represented less than 2% of the typical bodyweight of the geese. The primary tasks of the instrument were to continuously record a digitised ECG signal for heart-rate determination and store 12-bit triaxial accelerations sampled at 100 Hz with 15% coverage over each 2 min period. Measurement of atmospheric pressure provided an indication of altitude and rate of ascent or descent during flight. Geomagnetic field readings allowed for latitude estimation. These parameters were logged twice per minute along with body temperature. Data were stored to a memory card of 8 GB capacity. Instruments were implanted in geese captured on Mongolian lakes during the breeding season when the birds are temporarily flightless due to moulting. The goal was to collect data over a ten month period, covering both southward and northward migrations. This imposed extreme constraints on the design's power consumption. Raw ECG can be post-processed to obtain heart-rate, allowing improved rejection of signal interference due to strenuous activity of locomotory muscles during flight. Accelerometry can be used to monitor wing-beat frequency and body kinematics, and since the geese continued to flap their wings continuously even during rather steep descents, act as a proxy for biomechanical power. The instrument enables detailed investigation of the challenges faced by the geese during these arduous migrations which typically involve flying at extreme altitudes through cold, low density air where oxygen availability is significantly reduced compared to sea level.

Received 04 October 2013Accepted 09 December 2013Published online 02 January 2014

Acknowledgments:

We would like to thank our Mongolian colleagues who participated in the fieldwork and in particular Nyambayar Batbayar and Tseveenmyaday Natsagdorj for securing the necessary authorisation. The support of various colleagues from the University of British Columbia, the United Nations Food and Agriculture Program, the US Geological Survey, the University of Tasmania, and the University of Birmingham is gratefully appreciated. Particular thanks are due to Bev Chua DVM, who led the surgical team. This work was supported by the Bangor University and BBSRC Grant No. BB/F015615/1 awarded to Dr. C. M. Bishop and Professor P. J. Butler.